The present invention generally relates to semiconductor fabrication. More particularly, the present invention relates to a photolithographic device adapted to protect electrical contact portions of a wafer-in-process, as well as an intermediate wafer product created during a dual damascene process.
In the manufacture of integrated circuits (ICs), microlithographic techniques are used to pattern one or more layers of conductive circuitry on a wafer. Referring to the wafer 10 shown in FIGS. 1-2, one typical microlithography patterning technique is a dual damascene process, which begins with the formation of openings 19 in a first dielectric material structure 18. A conductive material is then deposited over the dielectric structure 18 and within the openings 19. A chemical mechanical polish (CMP) is used to ablate the conductive material from a top surface of the dielectric structure, leaving plugs of conductive material 20 within the openings 19.
A hard mask layer 14 and a second dielectric material structure 12 are respectively positioned over the first dielectric structure 18. Vias 16 are formed in the second dielectric structure 12 and the hard mask layer 14, the vias 16 extending to the conductive plugs 20. A photoresist material is then deposited over the second dielectric structure 12 and within the vias 16. With a photolithographic device, such as a semiconductor mask or a reticle, the photoresist material is exposed and then developed. Specifically, the wafer-in-process is etched to create a large open area. The remaining photoresist is then removed, and a conductive material 62 is deposited within the vias 16 and over the dielectric structure. A CMP of the conductive material may be performed to prepare the wafer 10 for further processing. The wafer 10 thus formed may be incorporated within a semiconductor device, such as a memory cell in a DRAM.
A disadvantage in the above-described method is that all of the photoresist material in the vias 16 is exposed and developed. This uncovers the electrical contact portions adjacent to the hard mask layer 14 (i.e., the conductive plugs 20) during the subsequent etching of the wafer-in-process to create the large open area. This may lead to possible damage of the hard mask layer 14 and/or the conductive plugs 20.
While seen in the fabrication of all wafers, this disadvantage is more prevalent when large circuitry is to be formed, such as in a large metal bus or a large bonding pad. Using a conventional photolithographic device for developing the photoresist material in wafers, the depth of focus (DOF) of the radiant energy is greater than the depths of the vias 16, and hence all the photoresist material within the vias 16 may be exposed and developed, or removed.
There exists a need for a photolithographic device which protects the electrical contacts of wafers-in-process during subsequent wafer fabrication processes.
An embodiment of the present invention provides a photolithographic device adapted for developing a portion of photoresist material on a wafer-in-process including vias within a dielectric layer overlain by the photoresist material. The device includes a radiant energy transparent portion and radiant energy blocking portions. The blocking portions are registered to the wafer-in-process to prevent direct radiant energy transmission to the photoresist material directly overlaying the vias.
Another embodiment of the present invention provides a system for fabricating a wafer including a source of radiant energy and a photolithographic device positioned between the source of radiant energy and a wafer-in-process including vias within a dielectric layer overlain with a photoresist material. The photolithographic device has a radiant energy transparent portion and radiant energy blocking portions. The blocking portions are registered to the wafer-in-process to prevent direct radiant energy transmission to the photoresist material directly overlaying the vias.
Another embodiment provides a method of fabricating a wafer including a plurality of conductive plugs in a first dielectric layer overlain by a hard mask layer and a second dielectric layer. The method includes forming vias in the second dielectric layer, each via extending to a corresponding conductive plug, applying a photoresist material to fill the vias and cover the second dielectric layer, and exposing a portion of the photoresist material so as to leave unexposed a second portion of the photoresist material located at a lower portion of the vias. The exposing includes using a photolithographic device which is adapted to prevent direct transmission of radiant energy to the photoresist material directly overlaying the vias.
Another embodiment provides a wafer-in-process including a first dielectric layer, at least one conductive plug within said first dielectric layer, a hard mask layer positioned atop said first dielectric layer, a second dielectric layer over said hard mask layer, at least one via extending through said second dielectric layer and said hard mask layer to said conductive plug, and photoresist material positioned only at a portion of said via adjacent said hard mask layer
The foregoing and other objects, features and advantages of the invention will be more readily understood from the following detailed description of preferred embodiments of the invention, which is provided in connection with the accompanying drawings.